It has become common to use concrete blocks for landscaping purposes. Such blocks are used to create, for example, retaining walls, ranging from small tree ring walls and garden edging walls to comparatively large structures. Concrete blocks are made in high speed production plants, and are often exceedingly uniform in appearance. This is not an undesirable characteristic in some landscaping applications, but it is a drawback in many applications where there is a demand for a “natural” appearance to the material used to construct retaining walls and other landscaping structures.
One way to make concrete blocks less uniform, and more “natural” appearing, is to use a splitting process to create a “rock-face” on the block. In this process, as it is commonly practiced, a large concrete workpiece which has been adequately cured is split to form two blocks. The resulting blocks have faces along the plane of splitting that are textured and irregular. This process of splitting a workpiece into two concrete blocks to create a rock-like appearance on the exposed faces of the blocks is shown, for example, in Besser's U.S. Pat. No. 1,534,353, which discloses the manual splitting of blocks using a hammer and chisel.
Automated equipment to split a concrete workpiece to form blocks is well-known, and generally includes splitting apparatus comprising a supporting table and opposed, hydraulically-actuated splitting blades. A splitting blade in this application is typically a substantial steel plate that is tapered to a relatively narrow or sharp knife edge. The blades typically are arranged so that the knife edges will engage the top and bottom surfaces of the workpiece perpendicular to those surfaces, and they are coplanar with each other. In operation, the workpiece is moved onto the supporting table and between the blades. The blades are brought into engagement with the top and bottom surfaces of the workpiece. An increasing force is exerted on each blade, urging the blades towards each other. As the forces on the blades are increased, the workpiece splits, generally along the plane of alignment of the blades.
These machines are useful for the high-speed processing of blocks. They produce an irregular, rock-face finish on the blocks. No two faces resulting from this process are identical, so the blocks are more natural in appearance than standard, non-split blocks. However, the edges of the faces resulting from the industry-standard splitting process are generally well-defined, i.e., regular and “sharp”. These concrete blocks can be made to look more natural if the regular, sharp edges of their faces are eliminated.
One known process for eliminating the regular, sharp edges on concrete blocks is the process known as tumbling. In this process, a relatively large number of blocks are loaded into a drum which is rotated around a generally horizontal axis. The blocks bang against each other, knocking off the sharp edges, and also chipping and scarring the edges and faces of the blocks. The process has been commonly used to produce a weathered, “used” look to concrete paving stones. These paving stones are typically relatively small blocks of concrete. A common size is 3.75 inches wide by 7.75 inches long by 2.5 inches thick, with a weight of about 6 pounds. The tumbling process is also now being used with some retaining wall blocks to produce a weathered, less uniform look to the faces of the blocks.
There are several drawbacks to the use of the tumbling process in general, and to the tumbling of retaining wall blocks, in particular. In general, tumbling is a costly process. The blocks must be very strong before they can be tumbled. Typically, the blocks must sit for several weeks after they have been formed to gain adequate strength needed for the tumbling process. This means they must be assembled into cubes, typically on wooden pallets, and transported away from the production line for the necessary storage time. They must then be transported to the tumbler, depalletized, processed through the tumbler, and recubed and repalletized. All of this “off-line” processing is expensive. Additionally, there can be substantial spoilage of blocks that break apart in the tumbler. The tumbling apparatus itself can be quite expensive, and a high maintenance item.
Retaining wall blocks, unlike pavers, can have relatively complex shapes. They are stacked into courses in use, with each course setback a uniform distance from the course below. Retaining walls must also typically have some shear strength between courses, to resist the pressure of the soil behind the wall. A common way to provide uniform setback and course-to-course shear strength is to form an integral locator and shear protrusion on the blocks. Commonly these protrusions take the form of lips (or flanges) or tongue and groove structures. Because retaining wall blocks range in size from quite small blocks having a front face with an area of about 0.25 square feet and weighing about 10 pounds, up to quite large blocks having a front face of a full square foot and weighing on the order of one hundred pounds, they may also be cored, or have extended tail sections. These complex shapes cannot survive the tumbling process. Integral protrusions get knocked off, and face shells get cracked through. As a consequence, the retaining wall blocks that do get tumbled are typically of very simple shapes, are relatively small, and do not have integral protrusions. Instead, they must be used with ancillary pins, clips, or other devices to establish setback and shear resistance. Use of these ancillary pins or clips makes it more difficult and expensive to construct walls than is the case with blocks having integral protrusions.
Another option for eliminating the sharp, regular edges and for creating an irregular face on a concrete block is to use a hammermill-type machine. In this type of machine, rotating hammers or other tools attack the face of the block to chip away pieces of it. These types of machines are typically expensive, and require space on the production line that is often not available in block plants, especially older plants. This option can also slow down production if it is done “in line”, because the process can only move as fast as the hammermill can operate on each block, and the blocks typically need to be manipulated, e.g. flipped over and/or rotated, to attack all of their edges. If the hammermill-type process is done off-line, it creates many of the inefficiencies described above with respect to tumbling.
Yet another option for creating a more natural block face appearance and eliminating the sharp, regular edges of concrete blocks is disclosed in commonly assigned, copending U.S. patent application Ser. No. 09/884,795 (filed Jun. 19, 2001), Ser. No. 09/691,864 (filed Oct. 19, 2000), and in U.S. Pat. No. 6,321,740, which are incorporated herein by reference in their entirety. As disclosed in these copending applications and patent, a splitting assembly is provided with a plurality of projections that are positioned to engage the workpiece during splitting to create an irregular upper and/or lower front edge on the resulting block. As is further described in commonly assigned, copending U.S. patent application Ser. No. 10/103,155 (filed Mar. 20, 2002) and Ser. No. 10/411,453 (filed Apr. 10, 2003), smaller projections in the form of a multiplicity of peaks can used in place of, or to supplement the action of, the larger projections to eliminate the sharp, regular edges of concrete blocks.